| 摘要 |
PURPOSE:To integrally manufacture a large-sized permanent magnet of 200g or more in weight without generation of cracks and chippings by a method wherein a reheating operation is conducted on the sintered body to the temperature lower by 300 deg.C from the sintering temperature, and after this state has been maintained for 10 minutes or longer, the sintered body is cooled down to the temperature which is lower by 500 deg.C or less from the sintering temperature at the cooling rate of 0.03 to 3 deg.C/min., and after it has been maintained for one hour or longer, it is gradually cooled down to about 400 deg.C or lower at the average cooling rate of 5 to 50 deg.C/min. CONSTITUTION:A sintered magnet body is cooled down to the desired low temperature which is lower by 300 deg.C than the sintering temperature, and after it has been maintained at that temperature for a specific period, the sintered magnet body is cooled down in a furnace under a protective atmosphere. The sintered body is maintained at the above-mentioned temperature for one hour or longer, desirably four hours or longer at the point of time when the sintered body is cooled down to about 500 deg.C or longer from the sintering temperature. Subsequently, it is taken out under protective atmosphere and placed in a stationary state until it is cooled down to about 300 deg.C or lower at the average cooling speed of 5 to 50 deg.C/min. |
